Military Flight Safety

chetak · Post by **chetak** » 05 May 2023 08:05

ks_sachin wrote:
chetak wrote:
predigested and prepackaged pap is not going to cut the mustard...

I still have an open mind, but now the anger is fast building, as indeed it is, with many across the country.

if what you say if true, then why the major embarrassment with these series of fiascos, especially when global attention is so keenly focused on these platforms and why did the updated SOPs not work..

In an event of this magnitude, a holistic and thorough reappraisal of all procedures should have been carried out. There was certainly enough time during the grounding to have done a very thorough and independent audit.

maybe it's also high time to do a deep and non partisan dive into what the PSU has been doing including the audits of it's suppliers, manufacturing, and storage procedures, QC, training, and maintenance, including the platform management philosophy

from what one is hearing, fingers are being pointed everywhere else except inwards, where the antiseptic light of honesty should have, first and foremost, shone with the greatest of intensity

If ever a manufacturer should have stepped in on their own, and gone above and beyond the call, to reassure their customers by finding safe and workable solutions and help to regenerate confidence, it is this PSU and at this time
Good for you. Let you anger build up. Let the IAF and PSU top brass take notes and implement your action plan. They don't know what they are doing it seems.

less about the top brass, either MIL or PSU. This is usually where the politics over rides flight safety.

I could do chapter and verse but this is an open forum

cool your jets, you have already been called out enough number of times

chetak · Post by **chetak** » 05 May 2023 08:08

ks_sachin wrote:
chetak wrote:

What is Error Proofing?

So you are saying we can completely eliminate human error?
Completely?
Completely like 0% chance?

you should know, bro

every time something is "idiot proofed", they just go ahead and invent a bigger idiot

my last on this

ks_sachin · Post by **ks_sachin** » 05 May 2023 09:26

I will assume that this was not you calling me an idiot. But I was actually alluding to the fact that the absolutes generally do not work in practice. In practice, training/commitment etc, all come into play, and not everyone has the same level of competence or commitment - a fact of life.

Anyway, my last too on this..don't want to be called out again, do I.

Pratyush · Post by **Pratyush** » 05 May 2023 10:05

Guys,

I don't know what's happening with the Dhruv fleet.

I know the following.

The aircraft had been in service for nearly 25 years. It has enjoyed a stellar safety record.

I request that we wait for the COI to finish it's investigation. Before jumping to conclusions and assigning blame.

nandakumar · Post by **nandakumar** » 05 May 2023 10:08

ks_sachin wrote:I will assume that this was not you calling me an idiot. But I was actually alluding to the fact that the absolutes generally do not work in practice. In practice, training/commitment etc, all come into play, and not everyone has the same level of competence or commitment - a fact of life.

Anyway, my last too on this..don't want to be called out again, do I.

ks_sachin
I can't presume to speak for chetak. But as I understood he was referring to the metaphorical assembly line worker who can somehow screw things up- pun unintended!

chetak · Post by **chetak** » 05 May 2023 10:22

Pratyush wrote:Guys,

I don't know what's happening with the Dhruv fleet.

I know the following.

The aircraft had been in service for nearly 25 years. It has enjoyed a stellar safety record.

I request that we wait for the COI to finish it's investigation. Before jumping to conclusions and assigning blame.

Pratyush ji

the unprecedented grounding of the ALH fleet should have resulted in some very tangible positive outcomes, but instead, a series of new fiascos have been the result.

At this point, the over all picture is very damaging

No one is saying shut down the line and/or import gora aircraft.

The ALH is a reasonably good platform but for a series of problems to emerge in quick succession, and at this late stage, possibly means that some recent changes in design/manufacturing/ supply chain issues /changes in aircrew SOPs /maintenance SOPs et all or even the changes to the platform management ecosystem may be areas which may need looking into

The manufacturer is conspicuous by the silence that they have chosen to maintain, primarily because they have an assured, as well as, a captive market that they see as feeding steadily into their income stream, for some decades to come..

It's very lucrative because it is usually a cost + 10% contract

The hunger in the belly comes from when they see the need to maintain/increase their market share and that usually results in excellence because of the need to innovate and out do the competition.

most monopolies do not normally see beyond their noses... and the bigger PSUs are slowly getting there

MeshaVishwas · Post by **MeshaVishwas** » 05 May 2023 12:41

Young aviation technician CFN Pabballa Anil has succumbed to his injuries sustained in today’s Army Dhruv helicopter crash in Kishtwar, J&K.

-Shiv Aroor on Twitter
Om Shanti

ramana · Post by **ramana** » 06 May 2023 05:49

Chetak
Any insight into how this new crash in Kistawar occured?

pravula · Post by **pravula** » 06 May 2023 06:13

Aren’t fleet grounding common in most air forces? How many times did F35 get grounded again? And there was an army wide grounding of all heli flights a week ago in US for procedural issues. Should they fire all army heli people and import new “models”?

chetak · Post by **chetak** » 06 May 2023 12:12

ramana wrote:Chetak
Any insight into how this new crash in Kistawar occured?

they have clamped down on all ALH news

basant · Post by **basant** » 06 May 2023 18:19

It's unfortunate to see Mao sir posting unfair comments. The ungrounding was done after the reasons were established, and yet this is what he says:

I hope, at least this time, someone learns the lesson that “far more important than how/how often you ground a fleet, what actually matters is how you unground (sic) it!”

What exactly does such a respected HAL TP needs more?

rrao · Post by **rrao** » 06 May 2023 19:20

Fresh water has replaced old water. ppl from various divisions apply for transfer ,and in the month April, transfers get effected.so old ALH designers must have long gone either retired are working in home div which may not be RWRDC or HC,BLR...SO how many ways an ALH can be made to crash?
1. loss of power in the engines, both or single due fire, fuel leak, flameout due to contaminated fuel
2. main rotor breakage/failure, tail rotor failure, loosening of bolts and nuts,
3. main gear box failure
4.controls failure ,control hinges failure
5.hydraulic failure, total electrical failure
6.failure due to inclement weather high winds, high temp,high altitude,
7. Just like that failure for unknown technical reasons...
8. Navigation aids failure due to which helo can crash during night flying
9. due to excessive engine vibrations
10. safety of flight envelope exceeded

experts can add more and letus check how many of ALH and other helos have crashed due to above reasons++

Jay · Post by **Jay** » 06 May 2023 20:17

basant wrote:It's unfortunate to see Mao sir posting unfair comments. The ungrounding was done after the reasons were established, and yet this is what he says:

What exactly does such a respected HAL TP needs more?

Basant ji, with how much Mao sir tried to elevate our products and walked the talk, I will give him the benefit of doubt. If he is really apprehensive about some thing, it might do us good to take a second look.

basant · Post by **basant** » 06 May 2023 21:05

Sir, I have immense respect for Mao sir. My gut feeling is that he is backing his colleagues trusting their gut feeling. However, the reasons behind the previous crashes have been established. It is possible that he suspects something else but is not able to mention. Having said that, the remark is snide and is uncalled for given the recent events where the 'experts' were wrong and couldn't wait to read the report. And could have waited for the report in this instance too.

I am sorry to say this, but it appears to me that some of the 'experts' believe there is something that is wrong and they could be right too. However, to keep bringing the same reasons over years despite many reports AND service record to the contrary leaves the impression of them waiting/wanting to be proven right rather than waiting to see if the actual experts (builders) have addressed the issue long back. This 'waiting' cannot be equated to 'salivating'..., however given their record of eerie silence on Mig-29Ks leaves little room for respect on the intent.

IN officers deserve respect for their service and expertise. However, that cannot be an adequate reason to run down the sacrifices by many in the R&D and production of HAL ecosystem.

Cyrano · Post by **Cyrano** » 06 May 2023 23:16

New Helis once delivery is accepted become services' property. One can always look for design and mfg flaws from HAL, but we also have the whole area of maintenance and care, training of pilots and ground crew, ATC, actual conditions of flying etc, including risk of sabotage. Maker's warranty vs Operator's responsibility if you will.

Grounding the fleet does not mean only HAL is under the scanner. It also means the services are looking into their own abilities to understand and operate a sophisticated piece of equipment in various conditions. Helis can be produced again, dead personnel cant be brought back. So suggest we trust both the makers and operators, and stop this heehaawing each time an unfortunate incident occurs and grounding happens.

ramana · Post by **ramana** » 08 May 2023 04:43

The thing to understand is there is a reason why it's called root cause analysis for causes are usually buried deep and need fault tree analysis and open mind without artificial deadlines.

For all we know this Kistawar accident cause could very well e different than the two other ALH crashes.
The problem is familiarity too often breeds contempt ie one rushes to judgment and that stops further analysis.
A fault tree is open till all branches are closed. Most often nuclear reactor and flight safety use fault tree process.

chetak · Post by **chetak** » 08 May 2023 04:53

https://www.hindustantimes.com/india-ne ... 21151.html

Army grounds Dhruv ALH fleet again following Kishtwar crash

ramana · Post by **ramana** » 08 May 2023 05:29

chetak wrote:https://www.hindustantimes.com/india-ne ... 21151.html

Army grounds Dhruv ALH fleet again following Kishtwar crash

Quite a rambling article by Rahul Singh who can do better. The worst is
"The helicopters have been riddled with problems including control rod failure (affecting power input to rotor blades) and hydraulics issues, the officials said."
How can that official says its riddled with control rod failure when it was a re-installation issue on the control rods in the IAF shop?
Such cretins should have the courage to give their names and be quoted.
It is the COI process of IAF that is the problem. They go thru the motions and close it up by blaming the pilot or mfg.
Does the IAF have a list of all the ALH crashes and COI reports in one place?
Doesn't the IAF AM in charge of helicopters seized of the need to get to the bottom of these crashes?
We know the ACM is busy with MRFA and the "Future is now" type of Muskisms.

I would hope ACM Chaudhri takes a page from Admiral D.K. Joshi and resigns when an ALH crashed right after the so-called exoneration after grounding the fleet.

chetak · Post by **chetak** » 08 May 2023 06:52

ramana wrote:
chetak wrote:https://www.hindustantimes.com/india-ne ... 21151.html

Quite a rambling article by Rahul Singh who can do better. The worst is
"The helicopters have been riddled with problems including control rod failure (affecting power input to rotor blades) and hydraulics issues, the officials said."
How can that official says its riddled with control rod failure when it was a re-installation issue on the control rods in the IAF shop?
Such cretins should have the courage to give their names and be quoted.
It is the COI process of IAF that is the problem. They go thru the motions and close it up by blaming the pilot or mfg.
Does the IAF have a list of all the ALH crashes and COI reports in one place?
Doesn't the IAF AM in charge of helicopters seized of the need to get to the bottom of these crashes?
We know the ACM is busy with MRFA and the "Future is now" type of Muskisms.

I would hope ACM Chaudhri takes a page from Admiral D.K. Joshi and resigns when an ALH crashed right after the so-called exoneration after grounding the fleet.

I think that they have a directorate of flight safety (or a similar organization but with a different name) where all such inputs are collated, analyzed and lessons learned are disseminated.

MeshaVishwas · Post by **MeshaVishwas** » 08 May 2023 10:19

I want to wait for CoI findings before rushing to judgements but I have a bone to pick with reports/"expert opinions" on Twitter that do that mistake.

HAL probably runs the highest mileage Dhruvs anywhere (based on this quote from a parallel ambitious program)

Flight testing follows a rigorous series of evaluations, culminating in generation of more than 19,000 pounds (84 kN) uninstalled thrust and completion of 330 hours of Accelerated Mission testing - the equivalent of 1,000 hours of flight operation.

-from GE
And if there was some sort of a glaring design flaw it would have been overcome by now.
If it's a question of technicians coming over to a tech fest that is Dhruv from a simpler machine like a Chetak/Cheetah, they may need to unlearn some habits.

MeshaVishwas · Post by **MeshaVishwas** » 08 May 2023 11:29

BREAKING: IAF MiG-21 crashes after take off from Suratgarh, Rajasthan. Pilot said to have ejected safely, but casualties reported on the ground. Details awaited.

2 civilians killed on the ground in today’s MiG-21 crash, reports
@IndiaToday
.

-LiveFist defence on Twitter
Heartbreaking accident.
Om shanti to the departed.

wig · Post by **wig** » 08 May 2023 12:08

https://www.msn.com/en-in/news/other/2- ... 12cd&ei=10

3 persons Dead as IAF's MiG-21 Aircraft Crashes on Their House in Rajasthan's Hanumangarh; Pilot ejects safely

video
https://www.msn.com/en-in/news/other/fo ... 95da&ei=16

sajaym · Post by **sajaym** » 08 May 2023 13:05

We have an indigenous fighter plane, of which a single one has not crashed in the past 20 years and yet we continue to use an old fighter which routinely crashes and now starting to fall on people's heads...the same people whom the IAF is supposed to protect. What's the sick logic behind this?!

basant · Post by **basant** » 08 May 2023 13:22

IAF will fight with whatever it has, but wouldn't order for desi products unless it has everything.

sanjayc · Post by **sanjayc** » 08 May 2023 13:56

MeshaVishwas wrote:I want to wait for CoI findings before rushing to judgements but I have a bone to pick with reports/"expert opinions" on Twitter that do that mistake.

HAL probably runs the highest mileage Dhruvs anywhere (based on this quote from a parallel ambitious program)
Flight testing follows a rigorous series of evaluations, culminating in generation of more than 19,000 pounds (84 kN) uninstalled thrust and completion of 330 hours of Accelerated Mission testing - the equivalent of 1,000 hours of flight operation.
-from GE
And if there was some sort of a glaring design flaw it would have been overcome by now.
If it's a question of technicians coming over to a tech fest that is Dhruv from a simpler machine like a Chetak/Cheetah, they may need to unlearn some habits.

Rarely do we hear of IAF Dhruvs crashing. Most crashes are from Army and Coast Guard. What gives? Maintenance and training issues with the latter two?

Manish_P · Post by **Manish_P** » 08 May 2023 14:16

wig wrote:https://www.msn.com/en-in/news/other/2- ... 12cd&ei=10

4 persons Dead as IAF's MiG-21 Aircraft Crashes on Their House in Rajasthan's Hanumangarh; Pilot ejects safely

video
https://www.msn.com/en-in/news/other/fo ... 95da&ei=16

Tragic.

Even if it is established that it was not his fault. the pilot will probably never get rid of the feeling of guilt.

Om shanti to the departed souls.

A Sharma · Post by **A Sharma** » 08 May 2023 21:19

Metallurgical Issue In Control Rod Flagged; Are ALH Dhruvs The New Flying Coffins?

The team of three armed forces personnel, who have been consulting with Hindustan Aeronautics Limited (HAL), has recommended that the current control rod be replaced with a stronger material, such as steel. The failure of control in the gearbox results in the helicopter not responding to pilot inputs, and pilots flying ALHs have reported sudden loss of power.

Tanaji · Post by **Tanaji** » 08 May 2023 21:49

Flying coffins… really? What irresponsible reporting…

ramana · Post by **ramana** » 08 May 2023 21:54

Who does maintenance for ALH?

Let's find out with real data.

basant · Post by **basant** » 08 May 2023 22:59

A Sharma wrote:Metallurgical Issue In Control Rod Flagged; Are ALH Dhruvs The New Flying Coffins?

The team of three armed forces personnel, who have been consulting with Hindustan Aeronautics Limited (HAL), has recommended that the current control rod be replaced with a stronger material, such as steel. The failure of control in the gearbox results in the helicopter not responding to pilot inputs, and pilots flying ALHs have reported sudden loss of power.

With a stronger material, such as steel? I am sorry, why would HAL have not used easily available material like steel if it solves all the problems? Who even wrote this report?

PS: The above question was rhetorical and not meant to offend anyone.

Pratyush · Post by **Pratyush** » 09 May 2023 08:17

I can understand that metals have a fatigue life and beyond that they are no longer fit for safe operations.

It is possible that the control rods were certified for certain flight hours. But due to manufacturing issues, they are failing before time.

But to make the claim that the control rod is a problem because it is made of aluminium. Is not understandable.

The reporting is not reflecting accurate facts. It's just FUD.

ramana · Post by **ramana** » 09 May 2023 09:22

Pratyush wrote:I can understand that metals have a fatigue life and beyond that they are no longer fit for safe operations.

It is possible that the control rods were certified for certain flight hours. But due to manufacturing issues, they are failing before time.

But to make the claim that the control rod is a problem because it is made of aluminium. Is not understandable.

The reporting is not reflecting accurate facts. It's just FUD.

Pratyush and Basant I think we can understand the problem.

1) The recent crash of an Advanced Light Helicopter (ALH) near Kishtwar, in the Jammu and Kashmir region, has once again 2) drawn attention to a metallurgical issue related to a crucial component: the control rod. 3) The control rod, which is made of aluminum, is located in the gearbox and is responsible for transferring power from the two engines of the helicopter to its overhead rotors.

4) The team of three armed forces personnel, who have been consulting with Hindustan Aeronautics Limited (HAL), has recommended that the current control rod be replaced with a stronger material, such as steel. 5) The failure of control in the gearbox results in the helicopter not responding to pilot inputs, 6) and pilots flying ALHs have reported sudden loss of power. To ensure safety, 6) special checks are in place to inspect the control rod after every 100 hours of flying.

First, the good news is that the Kistawar crash is not due to maintenance SNAFUs of incorrect control rods or serrated washers.
Second, the control rod material is an issue. HAL has used Al most likely a high-strength AL alloy. Aluminium has a brittle strength curve and has no yielding only ultimate strength.

Third the control rods transfer torque from the twin engines to the rear rotors. This means the rods are really shafts that see torsion loads.

So they could see fatigue failure due to torsion and bending. This could lead to crack creation and propagation.
To resist crack propagation the material has to have ductility or fracture toughness eg 4340 chrome molybdenum steel or Ti 6Al 4V.
Some Magnesium alloys of Aluminum have high ductility but not high strength.

HAl inspection of control rods every 100 hours is not enough to detect inherent damage from cracks for what the pilots report in 6) is a sudden loss of control due to rod shearing.
The failure is sudden and catastrophic.
All the crash reports should be re-opened to see what type of failure was seen.
Aluminum won't have the clean 45-degree shear plane we see in steel.
It will be brittle.

Even steel is not the answer unless it is a 4340 type of steel that has high fracture toughness.
If cost is not the issue and Titanium alloy is available then the preferred solution is this.

https://en.wikipedia.org/wiki/4340_steel

See the 11-23% elongation like taffy. That's what you need here to resist cracks.

4340 equivalent steel grade is 817M40 steel grade in BS 970-1991.

group Captain Hari Nair can you ask them what grade Al is used for the control rods?
I bet it's a 7075 rod type Al alloy.

I hope they are not using net factory dimension bars as they all have surface issues and need to be machined to take those out.

Prem Kumar · Post by **Prem Kumar** » 09 May 2023 10:11

The sudden string of failures after years of flying seems to indicate fatigue failure, as Ramana Ji said

If so, shouldn't it have been caught during fatigue testing by running it for 1000s of hours? CEMILAC also certified the flying machine. The root cause analysis should also go into what was missed during testing & certification. The Japanese 5-why's

Then, there was the other issue where rods were interchanged. As someone else pointed out here, its not just a training issue, but a design issue - in this case, "design for maintenance". Two rods, to be used in different parts of the machine, must be designed in a way that they are not interchangeable. An understandable miss in the design, but still something that needs to be fixed (though these would require extensive re-testing).

HAL, because of the unfair attack by the Import Bahadurs, is responding knee-jerk that all these problems are maintenance related. They don't seem to be. But they can take heart from the fact that these are normal during the course of an aircraft's lifecycle and nothing to be ashamed of. The fact that the Dhruv has flown lakhs of hours without incident is a testament to how robust the machine is. HAL's rotary division is an A-class unit and they have nothing to be ashamed of. The Import Bahadurs can be ignored - they are an incorrigible lot

But HAL needs to own up to problems and fix them. They owe it to our pilots & crew and they should also demonstrate that the OEM takes accountability

ramana · Post by **ramana** » 09 May 2023 10:23

Prem,
What's exasperating all failures are lumped together. What they need to do is separate the Control Rod failures and see how many there are and if there is any batch or melt issue with the Aluminium. And how many hours were flown with those control rods before failure?
The mis-installed control rods and the serrated or lock washers are maintenance issues.
A lock washer is installed under the nut so it can grip the surface and prevent loosening.

The jagged side should be to the bolt nut, not the washer. You're trying to prevent the bolt nut from turning, thus unscrewing. The jagged side will, to a small degree, bite into the metal of the bolt to increase the holding power.

This rod catastrophic failure is a design issue but won't show up unless lots of flying hours. The rods are misnamed and should be called shafts. They see torsion and bending loads. Shear won't show up in fatigue but combined with bending its bad. Example wagon wheels.
Another issue is I hope the rods get machined. The reason is in the rolling process there will be surface cracks. So usually need to machine a few thousand off to remove such surface imperfections. These are all nitty-gritty details.
Also, Five-Whys won't show this problem as it gives a surface look at the root cause.
Need a fault tree for aerospace issues.

chetak · Post by **chetak** » 09 May 2023 11:58

ramana wrote:Prem,
What's exasperating all failures are lumped together. What they need to do is separate the Control Rod failures and see how many there are and if there is any batch or melt issue with the Aluminium. And how many hours were flown with those control rods before failure?
The mis-installed control rods and the serrated or lock washers are maintenance issues.
A lock washer is installed under the nut so it can grip the surface and prevent loosening.

The jagged side should be to the bolt nut, not the washer. You're trying to prevent the bolt nut from turning, thus unscrewing. The jagged side will, to a small degree, bite into the metal of the bolt to increase the holding power.

This rod catastrophic failure is a design issue but won't show up unless lots of flying hours. The rods are misnamed and should be called shafts. They see torsion and bending loads. Shear won't show up in fatigue but combined with bending its bad. Example wagon wheels.
Another issue is I hope the rods get machined. The reason is in the rolling process there will be surface cracks. So usually need to machine a few thousand off to remove such surface imperfections. These are all nitty-gritty details.
Also, Five-Whys won't show this problem as it gives a surface look at the root cause.
Need a fault tree for aerospace issues.

If they have homed in on the right issue, there is no way that these rods should have passed fatigue tests in the first place

Pratyush · Post by **Pratyush** » 09 May 2023 12:11

Is it possible for a component to be designed for x fatigue life. But when it's been put in mass production, the product has only 0.8 or 0.9x fatigue life.

If it's possible.

Then how can this be reduced fatigue life be identified at the point of taking dilivery at the assembly line of the chopper?

chetak · Post by **chetak** » 09 May 2023 12:18

Pratyush wrote:Is it possible for a component to be designed for x fatigue life. But when it's been put in mass production, the product has only 0.8 or 0.9x fatigue life.

If it's possible.

Then how can this be reduced fatigue life be identified at the point of taking dilivery at the assembly line of the chopper?

The tests exceed the designed values by a considerable safety margin and many examples are tested to failure during the design stage itself to determine the ultimate limits

post manufacturing tests are separate and are also very comprehensive

The design itself is done taking into consideration a largish factor of safety

basant · Post by **basant** » 09 May 2023 12:56

^^^
It is necessary to find how many of the accidents/incidents are actually related to control rods. But at least from available stats until 2016, we can rule out 12 out of 16 of the crashes since 2002. I do not expect the helo to get away with such a failure, so I am not inclined to think that it may be part of incidents too. Additionally, the margins are generally kept on safer side for such critical components hence 100 hrs/inspection may be an overkill. But is it?

Let's see what is said by one of the prime critics, Cdr KP Sanjeev Kumar (Retd), in March 2023: "There have been at least four or five reported cases of sudden loss of control on the ALH due to breakages in flight control rods or boosters that provide longitudinal, lateral and collective control leading to accidents". Given that the previous year alone accounted 90,000 flight hours by about 300 Dhruvs, we can easily see that failure rate is infinitesimally low with 5 failures over 20+ years.

However, like Goebbels, "if you tell a lie big enough and keep repeating it, people will eventually come to believe it." Interestingly, he further added that, "the lie can be maintained only for such time as the State can shield the people from the political, economic and/or military consequences of the lie."

The fact that ALH has had darn good safety record despite operating under most challenging conditions over 21 years shows that 'control rods' may not be an issue. Can it be bettered, likely yes. But is it of suspicious quality, most likely not.

Jayram · Post by **Jayram** » 09 May 2023 13:55

ramana wrote:
Pratyush wrote:I can understand that metals have a fatigue life and beyond that they are no longer fit for safe operations.

It is possible that the control rods were certified for certain flight hours. But due to manufacturing issues, they are failing before time.

But to make the claim that the control rod is a problem because it is made of aluminium. Is not understandable.

The reporting is not reflecting accurate facts. It's just FUD.
Pratyush and Basant I think we can understand the problem.

1) The recent crash of an Advanced Light Helicopter (ALH) near Kishtwar, in the Jammu and Kashmir region, has once again 2) drawn attention to a metallurgical issue related to a crucial component: the control rod. 3) The control rod, which is made of aluminum, is located in the gearbox and is responsible for transferring power from the two engines of the helicopter to its overhead rotors.

4) The team of three armed forces personnel, who have been consulting with Hindustan Aeronautics Limited (HAL), has recommended that the current control rod be replaced with a stronger material, such as steel. 5) The failure of control in the gearbox results in the helicopter not responding to pilot inputs, 6) and pilots flying ALHs have reported sudden loss of power. To ensure safety, 6) special checks are in place to inspect the control rod after every 100 hours of flying.
First, the good news is that the Kistawar crash is not due to maintenance SNAFUs of incorrect control rods or serrated washers.
Second, the control rod material is an issue. HAL has used Al most likely a high-strength AL alloy. Aluminium has a brittle strength curve and has no yielding only ultimate strength.

Third the control rods transfer torque from the twin engines to the rear rotors. This means the rods are really shafts that see torsion loads.

So they could see fatigue failure due to torsion and bending. This could lead to crack creation and propagation.
To resist crack propagation the material has to have ductility or fracture toughness eg 4340 chrome molybdenum steel or Ti 6Al 4V.
Some Magnesium alloys of Aluminum have high ductility but not high strength.

HAl inspection of control rods every 100 hours is not enough to detect inherent damage from cracks for what the pilots report in 6) is a sudden loss of control due to rod shearing.
The failure is sudden and catastrophic.
All the crash reports should be re-opened to see what type of failure was seen.
Aluminum won't have the clean 45-degree shear plane we see in steel.
It will be brittle.

Even steel is not the answer unless it is a 4340 type of steel that has high fracture toughness.
If cost is not the issue and Titanium alloy is available then the preferred solution is this.

https://en.wikipedia.org/wiki/4340_steel

See the 11-23% elongation like taffy. That's what you need here to resist cracks.

4340 equivalent steel grade is 817M40 steel grade in BS 970-1991.

group Captain Hari Nair can you ask them what grade Al is used for the control rods?
I bet it's a 7075 rod type Al alloy.

I hope they are not using net factory dimension bars as they all have surface issues and need to be machined to take those out.

Hi Strength 7075 and the like AlCrMg alloys manufacturing process can interdouce PCG (peripheral coarse grain) formation in the material which can be difficult to detect due to manual effort required to obtain microstructure cross sections to determine the depth and size of the PCG. For this reason end users would want to shave off a certain amount of material esp in round extruded bars before service. However that introduces extra work at user level and is no guarantee of material quality free from failure defects above. That could be a factor here as well and depending on the manufacturer the formation of PCG is different since it depends on the things like the compression ratio from the billet to the final product, temp of extrusion, heat treatment etc. I know for sure HAL is probably looking at this and this is actually easier to detect after the accident in the failed component. My interaction with HAL was in the 90's in this specific area and I can tell you that the department and its engineers were very knowledgble and well aware of the implications of every accident in this area.

rrao · Post by **rrao** » 09 May 2023 15:04

ISRO'S FAILURE ANALYSIS BOARDS ARE FABULOUS. If failure occurs once, it never repeated in the next flight. likewise ALH also needs to analysed after crashes. design flaw, pilot error, loss of fuel,material flaw,fatigue, wear and tare , engine failure, electrical power failure, hydraulics malfunction etc.. HAL helicopter folks will never have time as they are always engrossed in MRO issue. Only thing is left RWRDC, which is filled with new comers. HAL mgmt should constitute high level committee on isro FAB levels and do post mortem for thorough failure analysis.